1. Field
The present invention relates to a microphone, particularly to a microphone in which an acoustic sensor and a circuit element are stacked.
2. Related Art
A microphone is used in various devices such as a mobile phone and an digital voice recorder. For example, in the microphone disclosed in U.S. Pat. No. 6,178,249, an acoustic sensor and an application specific integrated circuit (ASIC) are connected to each other through a bump contact, a space between the acoustic sensor and the ASIC is used as a back chamber, and a volume of the back chamber is adjusted by changing the height of the bump contact. In the microphone disclosed in U.S. Pat. No. 7,763,972, an acoustic sensor and a circuit element are stacked, a cavity is formed in the circuit element at a position corresponding to a thin film, and the cavity is used as a back chamber.
Nowadays, there is a demand for further downsizing in the microphone, particularly there is a demand for a low profile in which a whole height of the microphone is reduced. On the other hand, there is also demand to enlarge the volume of the back chamber in order to improve a signal-to-noise ratio (SNR) and a frequency characteristic in a low frequency band.
The volume of the back chamber is defined by the height of the bump contact in a configuration disclosed in U.S. Pat. No. 6,178,249, and the volume of the back chamber is defined by the volume of the cavity formed in the circuit element in a configuration disclosed in U.S. Pat. No. 7,763,972. Therefore, in order to enlarge the volume of the back chamber, the height of the microphone needs to be increased, and thus it is difficult to simultaneously achieve the low profile of the microphone and the improvement of performance.